It is an experience that alkali persalts in particular alkali carbonate peroxy hydrates (percarbonates), which are used to a large extent in detergents, tend to cake when they are stored for a longer period of time. Because of this caking tendency a hardening of the material and connected therewith a lump formation can occur, whereby the handling is rendered more difficult. Under unfavorable conditions the caking can lead, in extreme cases, to lumping of the material in sacks or silo assemblies in such a manner that a transportation by the usual load-carrying equipment is no longer possible.